The present invention relates generally to biosynthetic processes and organisms capable of producing organic compounds. More specifically, the invention relates to non-naturally occurring organisms that can produce the commodity chemicals isopropanol, n-butanol, or isobutanol.
Isopropanol is a colorless, flammable, three-carbon alcohol that mixes completely with most solvents, including water. The largest use for isopropanol is as a solvent, including its well known yet small use as “rubbing alcohol,” which is a mixture of isopropanol and water. As a solvent, isopropanol is found in many everyday products such as paints, lacquers, thinners, inks, adhesives, general-purpose cleaners, disinfectants, cosmetics, toiletries, de-icers, and pharmaceuticals. Low-grade isopropanol is also used in motor oils. The second largest use is as a chemical intermediate for the production of isopropylamines (e.g. in agricultural products), isopropylethers, and isopropyl esters. Isopropanol is manufactured by two petrochemical routes. The predominant process entails the hydration of propylene either with or without sulfuric acid catalysis. Secondarily, isopropanol is produced via hydrogenation of acetone, which is a by-product formed in the production of phenol and propylene oxide. High-priced propylene is currently driving costs up and margins down throughout the chemical industry motivating the need for an expanded range of low cost feedstocks.
Butanol, or equivalently, n-butanol, is a four carbon alcohol that is currently manufactured almost exclusively through the use of petrochemical raw materials. The main petrochemical process entails carbonylation of propylene to butyraldehyde, followed by catalytic hydrogenation to butanol. The demand for butanol is driven by its use for production of butyl acrylate and butyl methacrylate, both of which are employed in emulsified and solution polymers used in water-based latex coatings, enamels, and lacquers. Other application include its use as an intermediate for large volume chemicals such as butyl acetate and glycol butyl ethers, as well as it direct use as a solvent. Butanol also is being considered for potential application as a biofuel derived from renewable resources. Butanol has a wide range of properties that make it better suited as a fuel than ethanol. For example, butanol has higher energy content, lower volatility and hygroscopicity, can be shipped through pipeline infrastructure, can be used directly without blending, and can be blended with diesel or biodiesel.
Isobutanol is another colorless, flammable, four carbon alcohol that is being aggressively pursued as a biofuel. Currently, its major application is as a starting material for isobutyl acetate, a common solvent used in the production of lacquer and coatings and also as a flavoring agent in the food industry. Isobutyl esters are used in plastics, rubbers, and other dispersions. Additional applications for isobutanol include its use as a solvent in paint, varnish removers, and inks. Methods for isobutanol synthesis from petroleum derived feedstocks include oxo synthesis (Weber et al., Industrial & Engineering Chemistry Research, 62:33-37 (1970)) and Guerbet condensation of methanol with n-propanol (Carlini et al., J. of Molecular Catalysis A: Chemical, 220:215-220 (2004); Carlini et al., J. of Molecular Catalysis A: Chemical, 184:273-280 (2002); Carlini et al., J. of Molecular Catalysis A: Chemical, 200:137-146 (2003); Carlini et al., J. of Molecular Catalysis A: Chemical, 206:409-418 (2003)).
Thus, there exists a need to develop microorganisms and methods of their use to produce isopropanol, n-butanol, or isobutanol using low cost feedstocks. The present invention satisfies this need and provides related advantages as well.